Sunlight Requirements for Hardy Mums

Hardy mums bloom in dozens of colors.

As summer nears its end, fall-blooming flowers become the centerpiece of many home gardens. Hardy chrysanthemums, often called mums, (Chryrsanthemum spp.) are at the head of the list in this group, with many different flower types in dozens of colors to enhance your beds and borders. Mums grow outdoors year-round in U.S. Department of Agriculture plant hardiness zones 5 through 9 and can also be grown as annuals or indoors as houseplants.

Light and Blooming

The hardy mum is a bushy, herbaceous perennial that grows as a slowly spreading clump, usually 1 or 2 feet tall. Its flowers can be round and resemble pom-poms, flat with petals that mimic spoons, or spidery with very thin petals. The mum is a photoperiodic plant and needs a specific amount of light to develop flower buds. In late summer, when nights shorten to about 10 hours, the plant receives a signal that initiates bud set. In general, flowers start opening between six and 10 weeks later, depending on the variety.

Site Selection

Although shortening days in late summer are critical for a mum to bloom, the plant also depends on good light throughout the season to grow well and develop into a strong plant. The best site for a mum is one that gets full sun for the entire day, although the plant can tolerate some light shade. In areas with hot summer sun, a spot that gets a few hours of light afternoon shade can help prevent scorching of the plant. A mum needs a minimum of six hours of sun each day to grow properly and is a poor choice for a fully shaded location.

Other Lighting

Because the hardy mum is a photoperiodic plant, locating it near an artificial light source such as a street light or porch that's lit at night can interfere with its bloom cycle. You can also grow a potted mum indoors as a houseplant, placing it in a brightly lit, west- or south-facing window during daytime hours. When a mum is grown indoors, it's important to keep the plant in darkness after sundown from late summer into fall, to allow buds to set. You can give it properly timed lighting and stimulate flower production by growing the plant in an unused room or a basement, or move it into a closet each night.

Other Care

The hardy mum is an easy-to-grow plant that requires little special care. It grows in any type of garden soil but does best in soil amended with compost at planting. The plant needs even moisture, so providing extra water during dry spells is helpful. Although a mum doesn't require pruning, pinching back the growing tips of its stems helps the plant develop a bushy and well-branched form and leads to maximum flower production. Stop pruning in mid-July to allow all existing stems to set flower buds.

About the Author

Joanne Marie began writing professionally in 1981. Her work has appeared in health, medical and scientific publications such as Endocrinology and Journal of Cell Biology. She has also published in hobbyist offerings such as The Hobstarand The Bagpiper. Marie is a certified master gardener and has a Ph.D. in anatomy from Temple University School of Medicine.